Analysis of fields and forces in a permanent magnet linearsynchronous machine based on the concept of magnetic charge

Two-dimensional and three-dimensional field distributions produced by permanent magnets (PMs) of a permanent-magnet linear synchronous motor (PMLSM) are obtained in analytical forms, based on the concept of magnetic charge and the method of images. The determination of electromagnetic forces and parameters of this type of a motor is examined. The proposed method and the resulting simplified formulas are useful for the design and analysis of PMLSMs as well as for other types of PM motors. Calculated results compare favorably with the experimental results, and thus validate the assumptions and the analysis     

Analytical calculation of magnetic field distribution in the slotted air gap of a surface permanent-magnet motor using complex relative air-gap permeance

We present an analytical method for calculation of no-load magnetic field distribution in the slotted air gap of a surface permanent-magnet (PM) motor with radial or parallel magnetization. The method introduces the notion of complex relative air-gap permeance, calculated from the conformal transformation of the slot geometry, to take into account the effect of slotting. As a result, an accurate solution of both radial and tangential components of the flux density can be obtained which shows excellent agreement with the results of finite-element simulations. As an example of the effectiveness of the model, we present calculations of the back electromotive force and the cogging torque waveforms in a surface PM motor.     

Calculating the external magnetic field from permanent magnets in permanent-magnet motors-an alternative method

We present an alternative method for calculating the magnetic field from a set of permanent magnets in a permanent-magnet motor. The method uses a cylindrical coordinate system to model the geometry of the structure enclosing the magnets. A Fourier series expansion yields an alternative to the more familiar multipole expansion given in spherical coordinates. The expansion is developed by using Green's function in cylindrical coordinates. A technique called charge simulation allows computation of an equivalent point charge distribution. Finally, Coulomb's law is applied to express the magnetic scalar potential in a mathematically tractable form.     

Unsteady motion of a fluid near a disk rotating in a magnetic field

The effect of a magnetic field on the velocity distribution in a fluid close to an unsteadily rotating disk is investigated.Notation r, , and z coordinates in the radial, circular, and axial directions - t time - u, v, and w radial, circular, and axial velocity components - u₀ radial velocity of external potential flux - v₀ circular velocity of the disk - (t) angular velocity of the disk - p pressure - density - v kinematic viscosity - B₀ characteristic of the applied magnetic field - electrical conductivity of fluid - R and Z dimensionless coordinates in the radial and axial directions - =Z/2 dimensionless coordinate - T dimensionless time - U, V, and W radial, circular, and axial components of dimensionless velocity - P dimensionless pressure - a, , and ₀ constants with dimensionality t^–1 - m, n, and positive numbers - k =a constant - = = B ₀ ² / parameter characterizing the magnetic field     

On the magneto-hydrodynamic flow past a rotating disk in a fluid-particle suspension with a circular magnetic field

The flow of an incompressible, viscous, electrically conducting fluid with a suspension of inert particles over a rotating disk in the presence of a circular magnetic field is investigated. The governing equations of motion are reduced to a set of nonlinear ordinary differential equations by similarity transformations, and solved numerically by using least squares finite element method. The radial velocity of the panicles attains its maximum on the surface of the disk and the particles slip in the tangential direction. The flow boundary layer is thickened and the axial flow field is reduced as a result of the magnetic field. The particle density is maximum near the surface of the disk.     

Control of nonmagnetic particles using a magnetic field

Abstract

A force and/or torque are induced in a material under the imposition of a magnetic field. Their magnitudes are different from those acting on the surrounding materials because of the difference in their physical properties. Therefore, a magnetic field is a powerful tool for controlling a second phase in a mother phase such as particles suspended in a liquid. In this paper, we focus on two processes. The first one is a novel method of magnetic filtration in which schwertmannite particles in wastewater are controlled using a magnetic field. The second one is a refining process for a metallic alloy structure during solidification in which solid particles suspended in the liquid phase are controlled using the force excited by the simultaneous imposition of a magnetic field and alternating current.     

Nonaxisymmetric unsteady motion over a rotating disk in the presence of free convection and magnetic field

The nonaxisymmetric unsteady motion produced by a buoyancy-induced cross-flow of an electrically conducting fluid over an infinite rotating disk in a vertical plane and in the presence of an applied magnetic field normal to the disk has been studied. Both constant wall and constant heat flux conditions have been considered. It has been found that if the angular velocity of the disk and the applied magnetic field squared vary inversely as a linear function of time (i.e. as (1−λt*)⁻¹, the governing Navier-Stokes equation and the energy equation admit a locally self-similar solution. The resulting set of ordinary differential equations has been solved using a shooting method with a generalized Newton's correction procedure for guessed boundary conditions. It is observed that in a certain region near the disk the buoyancy induced cross-flow dominates the primary von Karman flow. The shear stresses induced by the cross-flow are found to be more than these of the primary flow and they increase with magnetic parameter or the parameter λ characterizing the unsteadiness. The velocity profiles in the x- and y-directions for the primary flow at any two values of the unsteady parameter λ cross each other towards the edge of the boundary layer. The heat transfer increases with the Prandtl number but reduces with the magnetic parameter.     

Determination of the temperature field in plate with a disk for a nonideal thermal contact between them

The problem of determining the stationary temperature field in a plate with a disk of arbitrary profile is discussed for the case of a nonideal thermal contact between the plate and the disk. Heat transfer according to Newton's law takes place between the plate and the ambient medium.     

Comparative thermal analysis of different rotor types for a high-speed permanent-magnet electrical machine

A thermal analysis of three different rotor constructions for a high-speed permanent-magnet electrical machine is performed. The first type of rotor has a carbon-fibre sleeve for retaining the magnets against the centrifugal forces and an aluminium shield for eddy currents. The other two rotors have retaining sleeves made of different titanium alloys and do not have additional eddy-current shields. The thermal analysis of the rotor types is performed using two completely different approaches. The first implemented method is a numerical-multiphysics one that couples computational fluid dynamics equations with heat-transfer equations. For better reliability of the analysis, a traditional thermal-network method is also implemented for estimation of the temperature distribution in the examined rotors. The accuracy of the aforementioned methods is verified using experimental results for the average temperature rise of the permanent magnets. The results obtained from the implemented methods show that although the rotor with a retaining sleeve made of titanium alloy Ti?6%Al?6%V?2%Sn does not have any eddy-current shield, it fulfils the thermal constraints and can be implemented for high-speed applications.     

Determination of plasma parameters with a probing magnetic field pulse

An experimental technique for the determination of electric conductivity and temperature of plasma is presented. The technique is based on comparing the signals that are produced by a pulsed magnetic field in the circuits of two probes located within the studied plasma and outside of it. The proposed technique for the measurement of plasma parameters was tested experimentally in the context of measuring the electric conductivity and temperature of plasma flux formed in cathode spots of a high-current pulsed vacuum arc with a magnesium cathode.     

5.25 inch floppy disk drive using perpendicular magnetic recording

5.25 inch high density perpendicular magnetic recording floppy disk drive has beer developed by employing new types of high saturation magnetization ring head, Co-Cr single layer medium with Ge underlayer, head slider with ellipsoidal surface configuration to assure intimate head to medium contact, and signal equalization. By these combination, recording density D50 of 145 kFCI, peakshift of 28 % at 100 kFCI, signal to noise ratio of 40.4 dB for cut-off frequency 4.25 MHz, overwrite signal to noise ratio of 27 dB, measured by writing signals at 48 kFCI over previously written 100 kFCI signals were obtained as typical recording characteristics. These results would indicate that floppy disk drive with 100 kFCI recording density has enough system margin by above-mentioned combination. In this paper, design and performance of newly developed floppy disk drive are described.     

Detailed study of the magnetic circuit in a longitudinal flux permanent-magnet synchronous linear generator

We present the results of a theoretical study of the magnetic circuit of a longitudinal flux permanent-magnet synchronous linear generator. In our study, we used a coupled field and circuit model solved by a time-stepping finite-element technique to analyze the machine. We investigated the effects of different permanent-magnet shapes and sizes, as well as different stator steel geometries. We noted a significant difference in performance for different magnet shapes. Our results also illustrate how small changes, on a millimeter scale, will affect the flux path, and thereby the overall performance of the machine, highlighting the importance of stator steel geometry.     

Time dependent rotational flow of a viscous fluid over an infinite porous disk with a magnetic field

Both the semi-similar and self-similar flows due to a viscous fluid rotating with time dependent angular velocity over a porous disk of large radius at rest with or without a magnetic field are investigated. For the self-similar case the resulting equations for the suction and no mass transfer cases are solved numerically by quasilinearization method whereas for the semi-similar case and injection in the self-similar case an implicit finite difference method with Newton's linearization is employed. For rapid deceleration of fluid and for moderate suction in the case of self-similar flow there exists a layer of fluid, close to the disk surface where the sense of rotation is opposite to that of the fluid rotating far away. The velocity profiles in the absence of magnetic field are found to be oscillatory except for suction. For the accelerating freestream, (semi-similar flow) the effect of time is to reduce the amplitude of the oscillations of the velocity components. On the other hand the effect of time for the oscillating case is just the opposite.     

Analytic approximate solutions of rotating disk boundary layer flow subject to a uniform vertical magnetic field

The present paper is concerned with the analytical solution of the boundary layer flow of a steady, laminar, incompressible, viscous and electrically conducting fluid due to a rotating disk. Within this purpose, the recently popular homotopy analysis method is employed, making it possible to obtain explicitly analytic expressions for Lighthill??s coordinate straining parameter c in terms of the magnetic field parameter m, first used in Ackroyd (J Eng Phys 12:207?C220, 1978) for the nonmagnetic case and recently studied to get the small perturbation and large asymptotic representations in Ariel (Z Angew Math Mech 82:235?C246, 2001) for the magnetic case. Making use of the outlined approach, the mean velocity profiles corresponding to a wide range of magnetic strength parameters are computed, and also explicit formulas are derived for several quantities of physical significance.     

Transverse motion of charged particle with oscillating charge in magnetic field

It is established that a particle bearing an oscillating electric charge can exhibit transverse drift in a homogeneous magnetic field. This drift has a resonance character and cannot be eliminated even at small amplitudes of charge oscillations.     

Practical equalizer for a perpendicular magnetic disk

We have developed a readback equalizer for a perpendicular magnetic disk with a commercial anisotropic magnetoresistive head for use with a PR4ML read channel with 8-9 coding. The transfer function of the perpendicular magnetic disk, derived by Fourier analysis, has a phase lag of 90/spl deg/ from that of the longitudinal magnetic disk. We defined the parameters of the equalizer by simulation. The equalized readback signal nearly satisfied Nyquist's first criterion. Using resistor-capacitor circuits that correspond to the simulated function, we obtained a byte-error rate of below 10/sup -7/. Comparing the effect of incorporating PR4 or PR1 as part of the equalizer, we observed that PR4 gave a lower bit-error rate than PR1. Thus, PR4 is an effective detection method for a perpendicular magnetic disk. It is suitable not only for longitudinal magnetic disks, but also for perpendicular magnetic disks.